The design of new, environmentally friendly, primary explosives to replace lead azide has been a major topic in the research of energetic materials for many years. The unacceptable toxicity of lead azide and its detonation products mandates replacement for both ecological and personal health reasons.
However, finding a suitable replacement for lead azide is complicated by the fact that very few materials have properties which make them useful as primary explosives: the combination of a material that will undergo a deflagration to detonation transition upon ignition, while still being relatively safe to handle is quite rare in chemistry, with relatively few initiatory primary explosives known.
Recently, only one compound has been shown to be a “drop in” replacement for lead azide; requiring no redesign of initiatory devices (detonators or blasting caps) with simple replacement of lead azide by the new material. This new material was created by Pacific Scientific Energetic Materials Company (“PSEMC”) and is copper(I) nitrotetrazolate or “DBX-1”. DBX-1 is described in U.S. Pat. No. 7,833,330 (“the '330 patent”); U.S. Pat. No. 8,071,784 (“the '784 patent”); and U.S. Pat. No. 8,163,786 (“the '786 patent”) and U.S. Publication Nos. 2012-0024178 (“the '178 publication”) and 2012-0077983 (“the '983 publication”), all of which are currently assigned to PSEMC. The '330, '784, and '786 patents and the '178 and '983 publications are hereby incorporated in their entireties herein by this reference. All the explosive requirements of DBX-1 are comparable to that of RD1333 grade lead azide in that it is of comparable sensitivity and as such, safety, and also of comparable initiating performance allowing for a material that possesses all the characteristics of lead azide without the associated toxicity.
The current synthesis of DBX-1 involves preparation and isolation of sodium 5-nitrotetrazolate, which is not commercially available, from 5-aminotetrazole followed by a second reaction step which reacts sodium 5-nitrotetrazolate directly with Cu(I) (U.S. Pat. No. 8,071,784) or with Cu(II) and an in-situ reductant (U.S. Pat. No. 8,163,786) to produce copper(I) 5-nitrotetrazolate.
There is a need to improve the efficiency of the chemical process by providing a method for preparation of DBX-1 directly from 5-aminotetrazole via a single reactor process which may eliminate the step of isolating the sodium 5-nitrotetrazolate intermediate, a potentially explosive intermediate step. The process delineated in this invention provides a method for converting commercially available 5-aminotetrazole directly to DBX-1 via a single reactor process.
A further advantage of this method is the efficiency in terms of copper. A reaction, commonly known in the industry as the Sandmeyer reaction and used to produce a 5-nitrotetrazolate, utilizes copper(II) to enhance substitution of the reactive diazonium intermediate. This copper is removed and discarded as copper oxide during isolation of the sodium 5-nitrotetrazolate. Additional copper(II) is then used to convert the sodium 5-nitrotetrazolate to DBX-1. The process employed in this invention utilizes the copper(II) associated with the Sandmeyer reaction as a reactant for the formation of DBX-1.